Gas chromatography (GC) is a physical method for the separation, identification, and quantification of chemical compounds. A sample mixture is injected into a flowing neutral carrier stream and the combination flows through a tube or chromatographic column. The inner surface of the column is coated or packed with a stationary phase. As the sample mixture and carrier stream flow through the column, the components within the mixture are retained by the stationary phase to varying degrees depending on the relative volatility of the individual components and on their respective affinities for the stationary phase. Different chemical compounds are retained for different times by the stationary phase. When the individual mixture components are released into the carrier stream by the stationary phase, the components are swept towards the column outlet to be detected and measured by a detector. The specific compounds in the components of the mixture can be identified and their relative concentrations determined by measuring peak retention times and peak areas respectively.
In the push for faster chromatography, the trend continues to be towards smaller, less thermally massive ovens. The oven temperature needs to be controlled at a specific rate. After one sample run is completed, the oven generally needs to be cooled down to the start temperature before another sample can be analyzed. To achieve faster cycle time and higher sample throughput, it is desirable to minimize the oven cool-down time. One method is to optimize the airflow into and within the oven both during heating and cooling. Engineering the airflow patterns is a challenge as visualization techniques are few and expensive. Most of the advances have been a result of trial and error.
Current solutions either passively or actively influence the airflow patterns into and within a GC oven during oven cool-down. For example, some GC ovens passively introduce fresh air into the oven by having the end of the intake duct situated directly behind the oven's stirring fan in a low-pressure region. This low-pressure region works to draw air in through the intake duct. With smaller GC ovens, a more active approach has been attempted to place the intake opposite the oven's stirring fan and to locate an additional boxer fan on the intake duct to force fresh air into the oven. A tradeoff exists in this design, however, because the boxer fan's placement forces the boxer fan to work against the oven's stirring fan. As a result, the stirring fan must be operated at only a percentage of its full power in order to not overwhelm the boxer fan during cooling.